Weil Mclain F39 Error Code

newguy101

Hi,

I just got a Weil McClain Aquabalance AB-120C boiler installed, with outdoor reset control.

Three times in the 2 weeks the boiler has been functional (but not running the whole time since we've had some warm weather) I have gotten an F39 error code. The manual calls this an outdoor sensor fault, and gives the following 2 causes and corresponding corrections:

Cause 1 - Sensor damaged or wiring shorted. Correction - Check the wiring or replace the sensor.

Cause 2 - Sensor disconnected after activating the sliding temperature. Correction - Reconnect the outdoor sensor or disable the sliding temperature.

The heat has not yet come on this AM. However, the last two times I got the F39 error (and maybe it has happened more times that I didn't notice), the heat did eventually come back on. That makes me think that I am dealing with Cause 2 and not Cause 1?

Can someone help me understand what the "sliding temperature" is? I don't see that defined anywhere in the manual.

I have contacted the contractor who installed the boiler, but I also want to understand as much as possible of this myself. This is a much more complicated heating system than I've ever had, and if it is going to have the tendency to just stop working and throwing error codes... I am going to need to have a better handle on what is going on. On a 46 degree morning, this is not that big of a deal, but if it were 10 degrees out, it'd be much more of a problem!

Thanks everyone in advance for any help. I've attached a picture of the system, in case that is helpful at all.

Andrew

flat_twin

https://www.weil-mclain.com/sites/default/files/field-file/Weil-McLain_AquaBalance-Series2_Manual_550100325_0419b-web.pdf


Fault 39 per the manual...
"Outside sensor out of normal operating range (short circuit or open circuit). If sensor goes in short circuit and this condition lasts for more than 10 seconds, error is generated. In case sensor is back to the normal operating range, error is gone. Normal operating range for the outside sensor is from -22°F till +158°F. With sensor broken in a way that he makes an open circuit, error will be generated only if a curve is selected: OTC will be disabled but heating mode will be possible .
In case 2 or more sensors are broken, controller will pick up the first that was outside the operating range. Resolving error situation can be achieved only if the sensors is within operating range again."

Outdoor temperature sensor resistance values are on page 91, figure 117. If you have an ohm meter you can verify the sensor is within range. You can also verify the sensor wiring is not shorted or open.

newguy101

I do have an ohm meter. I will attempt to do this this weekend.

mattmia2

My bet is on a bad connection to the wire that goes out to the sensor at one end or the other.